Protective intracellular gene therapy for HIV disease requires targeting expression of candidate genes to the cells that serve as the primary targets of HIV, namely macrophages and T helper cells, both of which express cell surface CD4 glycoprotein. We have recently identified regulatory elements involved in both positive and negative transcriptional regulation of the CD4 gene. We will define minimal CD4 regulatory sequences that can be used to attain expression in T helper cells and various monocyte/macrophage lineage cells. We will also seek to attain high level lineage-restricted expression by testing a variety of combinations of regulatory elements, some of which are being developed in Dr. Nabel's laboratory. We will use this information to develop vectors for retroviral transduction and for particle-mediated delivery that will direct expression of therapeutic candidates exclusively in the correct hematopoietic lineages after introduction into bone marrow stem cells and progenitors. We will work with Dr. Kohn to test and optimize these vectors in a murine bone marrow reconstitution system. If experiments in murine systems are successful, the vectors will be used to transduce HIV transdominant genes into human bone marrow cells in seropositive individuals.